Antennas are, by virtue of the physics of the art, generally large structures and not aesthetically pleasing. In addition, they are readily noticed by even the most casual observer. There has been very little attempt in the prior art to make any allowance for an antenna's aesthetic appearance or for its concealment apart from the field of mobile antennas (i.e., those mounted on an automobile or an aircraft).
However, a number of situations exist in which antennas are required that necessitate concealment or disguise of the antenna. Some of these situations include areas or neighborhoods that prohibit conventional-looking antennas; law enforcement use that requires concealment of antennas or other items that would draw unwanted attention; security and alarm installations where the antenna component must be concealed to prevent undue attention; other situations that require or prefer that the antenna be unobtrusive, concealed, or disguised at a fixed location.
One consideration in designing a concealed antenna is its overall size. The smaller the antenna structure, the more readily it can be concealed. Thus, a strong regard must be given to sizing the antenna such that it can be concealed. To aid in performance of the antenna, it should also be located as high as possible within the limits of being disguised as a common fixture; thus, rooftop fixtures are the most desirable emulations to embody the antenna.
The easiest way to disguise and conceal an antenna is to make it look like a common, existing structure upon which the antenna would normally be mounted upon. Actually functioning as an integral component of the existing structure further adds to the cloaking of the antenna.
An extensive study of rooftops of both commercial and residential buildings revealed that they universally have vent pipes mounted on the roof for the plumbing system. These vent pipes are standardized into three diameters and they vary in length from a few inches up to three feet above the surface of the rooftop. Thus, concealing the antenna as a common roof vent pipe is a natural unobtrusive method.
The following prior art reflects the state of the art of which applicants are aware and is included herewith to discharge applicant's acknowledged duty to disclose relevant prior art. It is stipulated, however, that none of these references teach singly nor render obvious when considered in any conceivable combination the nexus of the instant invention as disclosed in greater detail hereinafter and as particularly claimed.
______________________________________ INVENTOR ISSUE DATE ______________________________________ U.S. PAT. NO. Bailey 2,184,729 December 26, 1939 Halstead 3,523,251 August 4, 1970 Reid 3,551,916 January 5, 1971 Francis, et al 3,596,273 July 27, 1971 Self 3,683,393 August 8, 1972 Francis, et al 3,737,910 June 5, 1973 Kornbau, et al. 4,388,388 June 14, 1983 Siwiak, et al 4,442,438 April 10, 1984 Smith 4,661,821 April 28, 1987 Shelton, et al 4,814,783 March 21, 1989 Lalezari 4,816,836 March 28, 1989 Otsuka Japan 2-58904 February 28, 1990 Otsuka Japan 2-108394 April 20, 1990 ______________________________________
Foreshortening antennas has a long history in the prior art. The most prevalent methods are via helical elements or via loading elements or coils within the arms of the elements. U.S. Pat. No. 3,683,393 issued Aug. 8, 1972 to Aaron C. Self shows a helical dipole antenna in which both legs are shortened by means of fashioning them in a helix. The foreshortening via helices results in a physically-shortened antenna structure, but also causes the resulting bandwidth to be narrower than a common half-wave resonant dipole antenna. This bandwidth reduction is not desirable for antennas that cover a fairly wide range of frequencies; yet the helical shortening is desirable to keep the antenna within reasonable dimensions.
Many arrangements have been devised in the prior art to render an antenna unobtrusive. For example, it is a common practice to secure fine antenna wires to an automobile windshield. It is also known to conceal an antenna beneath a rug or to bury it underground. Household power wiring has also been used as an antenna.
While the prior art does show many schemes to conceal an antenna, the prior art does not show an antenna mounted on a vent pipe projecting from a roof whereby the antenna performs the dual function of acting both as a vent pipe and as a radiator of electromagnetic energy.
Three important advantages are gained in mounting the antenna as a vent pipe. Firstly, antenna performance increases with distance above ground. By utilizing the height of the roof an advantage is gained over mounting at ground or room level. Also, the need for a supporting mast is eliminated. Secondly, since the vent pipe is solidly mounted to the building it affords a secure mounting to resist high wind loading. It is common to see mast mounted antennas blown down after a wind storm. Vent pipes are securely mounted to the roof and do not sway with the wind. Thirdly, the antenna also functions as a vent and blends in with the roof profile which usually supports one of more vent pipes.
U.S. Pat. No. 3,551,916 issued Jan. 5, 1971 to James S. Reid shows a cylindrical monopole supported by a coaxially mounted vent pipe located on a boat. While the Reid antenna is mounted on a vent pipe, it is not concerned with concealing the antenna as in mounting it on a projecting vent pipe with the antenna itself being an extension of the vent.
Japanese patent 0058904 issued February 1990 to Sozo Otsuka shows an antenna concealed within a brick chimney. Because of the relatively large space available within the interior of the chimney, conventional antennas are mounted therein.